Process and apparatus for reclamation of abrasive grit

ABSTRACT

A process for cleaning and reclaiming abrasive grit which includes the steps of initially scrubbing the grit with a liquid detergent, then separating relatively light impurities and residual detergent from the grit by flotation. The grit is then rinsed with clean water, and the rinsed grit is introduced to a heating zone which is heated to a temperature exceeding about 1,000*F. In the heating zone, the grit is subjected to moving hot air currents and agitation, and particles of glass in the grit are agglomerated by fusion to relatively larger particles. Air current passed through the heating zone is directed to a cyclone where relatively fine particles of the grit are recovered. The apparatus in which the process of the invention is conducted includes a rotary vibrator screen for removing relatively dense particles of wood, metal and the like from the finer or smaller particles of abrasive grit, a whirlpool wash unit in which the abrasive grit is subjected to the cleaning action of a detergent, a pair of superimposed sequential washing rotary flotation tables, elevator means receiving abrasive grit from the lowermost rotary flotation table and an elongated low temperature furnace mounted for rotation about its longitudinal axis, and inclined with respect to the horizontal at an angle of between 5* and 15*. Finally, the apparatus includes means for moving air through the low temperature furnace, and a cyclone separator interposed in the air flow thus developed.

United States Patent [191 Jackson 1 1 PROCESS AND APPARATUS FOR RECLAMATION OF ABRASIVE GRIT Filed: Dec. 3, 1971 Appl. No.: 204,420

[52] U.S. Cl 134/10, 134/19, 134/25 R, 134/40, 134/68, 134/104, 134/153, 209/444 [51] Int. Cl B08b 7/04, C23g 3/00 [58] Field of Search 134/10, 19,25 R, 33, 40, 134/104, 68, 153, 109, 161, 162; 34/133; 209/162, 444; 241/20, 68; 51/309 [56] References Cited UNITED STATES PATENTS 3,544,369 12/1970 Keogh 134/25 1,029,933 6/1912 Jones 209/444 1,359,105 11/1920 Richards.... 209/444 1,536,173 5/1925 Webb 209/444 2,477,948 8/1949 Allen 134/109 UX 2,515,194 7/1950 Christensen i. 241/68 X 3,639,172 2/1972 Keogh 134/25 OTHER PUBLICATIONS Million BTU Burner Aids Reclamation," Blue Blaze, Lone Star Gas Co., publisher, May; 1969, p. 7

Primary E.\'z1nziner-M0rris O. Wolk Assistant Examiner-T. W. Hagan Attorney, Agent, or Firm-Dunlap, Laney, HesSin & Dougherty [57] ABSTRACT A process for cleaning and reclaiming abrasive grit which includes the steps of initially scrubbing the grit with a liquid detergent, then separating relatively light impurities and residual detergent from the grit by flotation. The grit is then rinsed with clean water, and the rinsed grit is introduced to a heating zone which is heated to a temperature exceeding about l,O00F. In the heating zone, the grit is subjected to moving hot air currents and agitation, and particles of glass in the grit are agglomerated by fusion to relatively larger particles. Air current passed through the heating zone is directed to a cyclone where relatively fine particles of the grit are recovered. The apparatus in which the process of the invention is conducted includes a rotary vibrator screen for removing relatively dense particles of wood, metal and the like from the finer or smaller particles of abrasive grit, a whirlpool wash unit in which the abrasive grit is subjected to the cleaning action of a detergent, a pair of superimposed sequential washing rotary flotation tables, elevator means receiving abrasive grit from the lowermost rotary flotation table and an elongated low temperature furnace mounted for rotation about its longitudinal axis,and inclined with respect to the horizontal at an angle of between 5 and 15. Finally, the apparatus includes means for moving air through the low temperature furnace, and a cyclone separator interposed in the air flow thus developed.

4 Claims, 4 Drawing Figures PATENIEDAPR 9:914

sum 2 BF 2 O OOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOO 000000000000 OOOOOOOOOOOOOOO O OOOOOOOOOOOOOOOOQOO OOOOOOOOOOOOO OOOOO I llk BY I I/ PROCESS AND APPARATUS FOR RECLAMATION OF ABRASIVE GRIT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the cleaning and reclamation of spent abrasive grits of the type used for abrading and cleaning operations. More particularly, but not by way of limitation, the present invention relates to a method and apparatus for reclaiming aluminum compound-type abrasive particles after such particles have been utilized for abrading or cleaning various types of surfaces, and in particular, metal surfaces.

2. Brief Description of the Prior Art Various types of particles are used industrially for cleansing and polishing surfaces by abrasive action, or for abrading away surfaces to change the dimensions of various structural members. With some types of abrasive particles, a single usage destroys the abrasive properties of the particles so that they are no longer suitable for repeated usage in this way. Other types of particles do not suffer destruction of their abrasive characteristic in the manner described, and may be reutilized in the absence of chemical change or physical contamination with impurities which impair their usefulness on the surfaces to be cleaned or polished upon reuse.

Among the abrasive grits in widespread industrial use which have the ability to retain their abrasive characteristic are the aluminum-containing grits, including natural or synthetic alumina (aluminum oxide), and silicon carbide. These materials are widely used'for cleaning and polishing operations, particularly in the aircraft industry, and are extremely hard and have high melting points. Alumina has a hexagonal crystalline structure, and its planes of cleavage are such that it fragments or fractures along these lines of cleavage in such a way that its cutting or abrasive properties are retainedby the smaller particles developed upon fracturing.

In many industrial usages of aluminum oxide abrasive grit for cleaning and polishing, the grit becomes contaminated with particles of iron or steel, small particles of cellulosic material, such as paper or wood, moisture, grease and other foreign materials. In some industries, such as the aircraft industry, the various abrasives used from time to time, such as glass beads, walnut shells and aluminum oxide, are recovered from a common situs of usage through the same ducting, etc., with the result that the spent alumina is contaminated with particles of glass, walnut shells, etc. It has been a widespread practice to discard the spent aluminum oxide abrasive grit, or to at least employ it for other utilizations than the original usage of cleaning and polishing. In the aircraft industry, certain standards of purity are required to characterize new aluminum oxide abrasive grit intended for certain cleaning and polishing usages. After utilization, the level of contamination with the described foreign materials and impurities is such that the grit is no longer suitable for the usage and does not meet the described standards. Discarding of this spent abrasive grit, or a substantial economic downgrading thereof as a result of such contamination results in a significant economic loss. While efforts have been made in the past to process spent abrasive grit of this type to reducev the contamination thereof, no acceptable process for restoring the grit to the high level of purity of the fresh material has, to my knowledge, been developed.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention provides a method and apparatus for reclaiming contaminated abrasive grits or parti- Broadly described, the process of the invention comprises initially passing the contaminated grit through a physical classification device, such as a rotary screen, to remove from the grit relatively large particles of contaminants, and particularly, pieces of wood or other cellulosic material. The abrasive grit is then passed into a first cleaning zone where it is contacted, under agitation, with a liquid detergent which functions to remove dirt and grease adhered to or entrapped in the mass of grit particles. After the detergent cleaning action, the particles of grit are advanced to a first rotary flotation table where the abrasive particles are rinsed with water to remove detergent therefrom and undergo hydraulic particle separation. to remove relatively light particles of foreign matter from the grit by flotation. The abra sive grit particles are then removed from the first rotary flotation table to a second rotary flotation table where the grit is subjected to a clean water rinse to remove residual detergent, and also any light, relatively less dense contaminants which may not be removed on the first table.

From the second rotary flotation table, the particles of abrasive grit are conveyed by suitable conveyor to a low temperature adhesion furnace. In the adhesion furnace, the particulate abrasive material is subjected to agitation, concurrently with heating to a temperature exceeding 300F, and preferably exceeding 400F. Simultaneously, a current of hot air is directed in a countercurrent fashion through the grit to remove moisture and very fine particles of the grit. The air current, moved through the furnace, is directed through a cyclone where any entrained very fine particles of grit are separated from any less dense materials carried in the air current. The heavy particles of grit and agglomerated particles of glass are then removed from the grit by particle size classification, such as by screening. Fi-

nally, if contamination with fine particles of ferrous metals is involved, magnetic particle separation may be nonmagnetic particles of grit. 7

It is an object of the present invention to reclaim abrasive grit by restoring it to'a condition suitable for industrial cleansing and abrasive usages in which low contamination of the grit is required.

Another, and more specific, object of the invention is to remove grease, cellulosic and glassy contaminants from metallicabrasiv'e particles.

Another object of the invention is to reclaim spent aluminum oxide abrasive particles by the efficient removal of various contaminants therefrom.

Another object of the invention is to reclaim alumina abrasive grit by the removal of various contaminating materials therefrom, and in the course of such reclamation, to effect a desirable classification of the grit on the basis of particle size so that selective usage of the classi- BRIEF DESCRIPTION OF THE DRAWINGS v FIG. 1 is a'partially schematic illustration of one embodiment of the apparatus and system utilized in reclaiming abrasive grit in accordance with the process of the present invention.

FIG. 2 is a sectional view taken along line 2-2 of FIG. I.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1 and showing details of the rotary vibrator screen used in the invention.

FIG. 4 is a sectional view taken along line 44 of FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION In FIG. 1 of the drawings, a hopper for receiving spentor contaminated abrasive grit in a relatively dry state from a chute 12 is illustrated. A second chute 14 is used for delivering'moist or wet contaminated abrasive grit to the system of the invention. From the dry grit hopper 10, the grit is passed through a suitable metering valve 16 to a conveyer 18. The conveyer- 18 moves the relatively dry, contaminated abrasive grit into a-hood 20 which serves to confine airborne fines of very light weight which are stirred up by the agitation of the conveyer and a screening device subsequently used in the process, and to permit these airborne fines to be drawn off or ducted through a duct 22 and conveyed thereby into a suitable cyclone 24 to collect these fines and discharge them through a suitable valve 26 to a point subsequently in the process as hereinafter described.

'Within the hood 20 is located a rotary vibrator screen assembly designated generally by reference numeral 28. The rotary vibrator screen assembly 28 includes a framework which carries an internal screen 32 of frustoconical configuration and having openings therethrough of about /8 inch in diameter. An external or outer screen 34 is supported on thefra'm'ework and extends concentrically around the inner screen 32. The outer screen 34 is characterized in having openings therethrough of about 3/32 inch in diameter; At its end opposite the end into which the conveyer 18 projects, the rotary vibrator screen 28 includes an open-ended cylindrical metallic portion 36 which receives the overage from the screens 32 and 34. A yieldable, spring loaded vibrator arm 38 extends into the open end of the metallic portion 36 and yieldingly contacts the vanes of a spider 40 (see FIGS. 3 and 4). The overage from the vibrator screen 28 enters a chute 42 which discharges into a suitable waste hopper 44.

ln the operation of the rotary vibrator screen 28, the dry abrasive grit is received in this screen which is conging or choking of the external screen by screening from the mass of relatively dry abrasive grit, relatively large particles of cellulosic materials, such aswood chips, sawdust, paper particles and the like. This overage of contaminant materials enters the large end of the rotary vibrator screen assembly 28 and is removed from this location by the chute 42 to the waste hopper 44. The arm-38 periodically striking the vanes of the spider 40 vibrates the assembly and the material passing therethrough to prevent balling or agglomeration of the material, and to aid in preventing clogging of the screens.

The abrasive grit which passes through the screens 32 and 34 is passed into a Whirlpool wash unit 48. The whirlpool wash unit has a generally cylindrical upper portion and a frustoconical lower portion which communicates with a chute containing a metering valve 50. Wash water is conveyed to the central portion of the whirlpool wash unit 48 by a suitable wash water conduit 52. Before the wash water enters the whirlpool wash unit 48, liquid detergent is injected into the wash water stream from a suitable conduit 54. The amount of detergent introduced to the stream of wash water is controlled by a suitable valve 56. Within the whirlpool wash unit 48, the aqueous detergent solution is constantly agitated by a stirrer S8 driven by a motor 60.

tinuously driven in rotation by a suitable electric motor,

46, and the dry abrasive grit is moved slowly by gravity towards the relatively large end of the rotary vibrator screen assembly 28. In the course of this movement, an

initial screening action is performed by the internal screen 32, and a final screening action by the external screen34. The internal screen helps to preventclog- The stirrer 58 is constructed and oriented in the whirlpool wash unit 48'so as to cause currents of the detergent solution to circulate in a vertical direction inside the wash unit.

abrasive grit, and thus this material can be more easily passed to the whirlpool wash unit without ing than can the dry abrasive grit.

Within the whirlpool wash unit 48, the abrasive grit is subjected to a whirling lifting action in which it is lifted up from the center of the conical bottom toward the top of the unit and is propelled then by centrifugal force of the whirlpool created in the unit outwardly toward the confining walls of the unit. It then descends along these walls to the conical bottom. The flow out of the whirlpool wash unit 48 is metered by adjustment of the metering valve 50. A float not shown senses the level of liquid in the unit 48 and controls the degree of closure of solenoid valve 56 to maintain a constant desired liquid level in the unit. It may be noted that many abrasive grits, such as alumina, have relatively high speciflc gravities. In the case of alumina, the average specific gravity is about 4.0. I

The abrasive grit from the whirlpool wash unit 48 is discharged through the metering valve 50 on to the apex of a conical member carried by, and forming a part of, a rotaryflotation table assembly designated prior screengenerally by reference numeral 64. As shown in FIGS.'

annular lip 70 which projects upwardly. In the illustrated embodiment of the invention, the lip 70 is 2 inches in height. The table has a diameter of 36 inches, and the cone is 24 inches in diameter at its base. The table 66 is mounted on a supporting plate 72 which is driven in rotation by a suitable shaft 74 secured thereto at a central point. The shaft 74 is driven in rotation by a drive chain 76 engaging a sprocket 78 keyed to the lower end of this shaft. The chain 76 is driven by a suitable motor 80 which is also used to drive another rotary flotation table assembly as hereinafter described.

The rotary flotation table 66 is positioned in an open topped overflow tank 82 which has an inclined bottom permitting the tank to discharge through a pipe 84. As the detergent solution containing washed abrasive grit isdischarged from the, whirlpool wash unit 48 onto the apex of the cone 68 forming a portion of the rotary flotation table assembly 64, the detergent solution, of course, fills the volume defined inside the lip 70 of the rotary table and overflows this lip. The rotation of the table, coupled with the spreading effect of the cone 68 causes the solid particulate material including the abrasive grit to be moved radially outwardly toward the peripheral edge of the table 66. The relatively more dense material, including the abrasive grit particles and particles of metal and glass, deposit on the table after sinking downwardly through the detergent solution. The less dense, flotable materials move to the surface of the liquid, and flow over the top of the lip 70 and fall downwardly with the solution into the overflow tank 82. From the overflow tank 82, detergent solution containing light contaminant materials flows through the pipe 84 to a suitable filtering system (not shown) where the solid contaminants are removed from the detergent solution. The detergent solution is then recycled to the pipe 54 for introduction again to the whirlpool wash unit-48.

The abrasive grit which has been deposited on the upper surface of the table 66 beneath the surface of the liquid carried thereon is moved outwardly toward the peripheral edge of the table by the centrifugal force acting as the table is slowly rotated. Also deposited on the outer peripheral portion of the table 66 are abrasive grit particles from the cyclone 24. Projecting downwardly into contact with the table 66 is a chute 86. The chute 86 has a small bend therein to permit it to clear the peripheral lip 70 of the rotary flotation table assembly 64, and then has a downwardly inclined portion 86a which extends to amanifold 104 positioned over a second rotary flotation table assembly 90;

It will be noted in referring to FIG. 2 that the chute 86 opens onto the table 66 so that, as the table 66 is ro-' tated in the counterclockwise direction as shown in FIG. 2, abrasive grit carried on the table tends to be moved into the open end of the chute. To aid in the movement of the abrasive grit onto the chute 86 and over the angulation therein, a pipe 89 having downwardly projecting perforations formed therein extends over the table 66 and a portion of the chute 8 6 and from these perforations, jets of water play upon the table and the chute in a direction to force abrasive grit onto the chute and over the angulation in the chute formed for the purpose'of clearing the lip 70.

A second rotary flotation table assembly 90 is constructed somewhat similarly to the rotary flotation table assembly 64. It thus includes a conical member 92 mounted centrally upon a flat, horizontally extending v an endless belt or chain 112' which carries thereon a I table 94 which is driven in rotation by a shaft 96 secured centrally to the lower side thereof. The shaft carries a sprocket 98 which is engaged by the chain 76 hereinbefore described. The sprocket 98 is of the same size as the sprocket 78 used for driving the rotary flotation table assembly 64 so that the tables 66 and 94 are driven at equal speeds of rotation. The dimensions of the tables 66 and 94 are the same. At its outer periphery, the table 94 carries an annular lip 100 which is about 4 inches in height in a preferred embodiment of the invention, and thus has twice the vertical dimension of the annular lip surrounding the rotary table 66. The rotary flotation table assembly further includes an overflow tank 102 which receives liquid flowing over the lip from the table 94. The bottom of the overflow tank 102 in inclined so as to permit the contents of the tank to drain through a discharge conduit 103 into a-collection tank 105. From the collection tank 105, very small fines of abrasive grit (referred to end connected to an annular manifold 104 which receives the grit and discharges it through an arcuate opening l06.formed in one side of the manifold-The grit and the water in which it is carried gravitates down one side of the cone 92 onto the table 94. The cone 92 is continuously washed clean and water is supplied to the space enclosed by the lip 100 by means of an annular wash ring 108 having perforations in the lower side thereof which direct water downwardly onto the cone 92. The wash ring 108 may suitably be mounted around the manifold 104 as depicted in FIGS. 1 and 2.

Extending over the edge of the lip 100 and into close proximity to the upper surface of the table 94 is a drag elevator assembly, designated generally by reference numeral 110. The drag elevator assembly 110 includes plurality of outwardly projecting teeth 1 14. The. endless belt or chain 112 passes over a drive roller 116 and a pair of idler rollers 118 and 120. It will be noted in referring to FIGS. 1 and 2 that the teeth 114 of the drag elevator assembly 110 pass in close proximity to the upper surface of the table 94 and are oriented so that these teeth will pick up and carry upwardly on the drag elevator assembly, the accumulated particles of abrasive'grit which are moved against the lower end of the drag elevator assembly by the rotating table 94. It will be notedin referring to FIG. 2 that the discharge opening 106 the manifold 104 is oriented with respect to the lower end of the drag elevator assembly 1 10 so that abrasive grit is discharged down the side of the cone 92 onto a portion of the table 94 which, considering the direction of rotation of the table, has furthest to travel before arriving at the pickup end of the drag elevator assembly. This affords maximum opportunity for washing of the particles of abrasive grit before being depositedagainst the drag elevator assembly and picked up by the teeth 114 thereof.

Abrasive grit falls from the upper end of the drag elevator assembly 110 onto a slide 124 and moves down I the slide into a low temperature rotary furnace assembly designated generally by reference numeral 126. The low temperature rotary furnace assembly 126 ineludes a cylindrical furnace housing 128 which is mounted with its longitudinal axis extending at an angle of between and with respect .to the horizontal, and preferably at an angle of about 8 to the horizontal. The furnace housing 128 is supported in suitable bearings or trunnions 130 and 132, and is driven in rotation about its longitudinal axis by a suitable motor 134. The motor 134 drives a gear 136 which meshes with an annular gear ring 138 carried by'the cylindrical housing 128. A plurality of axially extending, circumferentially spaced mixer flights 139 are secured around the internal wall of the cylindrical housing 128.

At its upper end, the furnace housing 128 opens into a hood 140 which is vented through a duct 142 to the upper end of a cyclone 144. The overhead discharge from the cyclone 144 is passed through a filter element 146 and is drawn through a suction fan 148 driven by a motor 150. The suction fan 148 discharges to the atmosphere. At its lower end, the furnace housing 128 opens into a hood 152 in which is mounted a blower burner-assembly 154 which directs a jet of flame into the discharge end of the furnace housing 128, and which also cooperates with the suction fan 148 in creating a significant air flow through the. furnace housing. Material discharged from the lower end of the furnace housing 128 passes through an opening in the lower portion of the hood 152 and gravitates into a cooling drum 158 where the abrasive grit and other material discharged from the furnace is cooled.

OPERATION In the operation of the apparatus referred to in the dry state is introduced to the processof the invention via the chute 12. From the hopper 10, the dry grit is discharged onto the conveyor 18 which moves the relatively dry grit into the rotary screen assembly 28 located. in the hood 20. Airborne fines in the hood 20 are removed through the duct 22 to the cyclone 24 where they are taken out of the air and directed through a suitable pipe 27 to the table 66 forming a portion of the first rotary flotation table assembly 64.

Inthe rotary vibrator screen assembly 28, relatively large particles of paper, pieces of wood, chunks of metal, walnut shell particles (sometimes mixed with the grit for cleaning operations) and the like are screened from the abrasive grit and are passed out of the screen assembly onto a chute 42 which delivers these foreign materials to a waste hopper 44. The screened grit passes from the rotary screen assembly 28 into the whirlpool wash unit 48. Here the grit is subjected to inbeing introduced to this unit, so that the ievel of mate- 'rial in the unit remains substantially constant.

Abrasive grit tends to move outwardly on the table 66 and to accumulate toward the outer peripheral edge thereof. From this location, it is scooped up by the open end of the chute 86 and is moved into the-chute by the jets of water directed downwardly from the pipe 89. The abrasive grit is washed down the downwardly inclined portion 86a of the chute 86, passes through the manifold 104, and is discharged through the opening formed on one side of the manifold at a location on one side of the cone 92. From this location, the grit isdeposited upon the rotary table 94 at a locus which is se lected to permit the grit to move through the major portion of one full rotation of the table before arriving at the point where the grit is picked up by the drag elevator assembly 110.

on the table 94, the grit is further washed by water jetted downwardly on the table from the annular wash ring 108, and this water also functions to clean the surface of the cone 92. The function of the rotary flotation table assembly 90 is to dilute residual detergent solution carried onto the table by the abrasive grit, and to remove this detergent solution from the grit. Actually, some very small abrasive gritparticles are caused to wash over the lip 100 (which extends around the periphery of the table 94) into the overflow tank 102 and tense agitation'and contact with a detergent solution.

The detergent utilized is a strong surfactant material added 'tothe incoming wash water via the conduit 54. Wet or damp abrasive grit may also be introduced to the whirlpool wash unit 48 from the pipe 14.

In the whirlpool wash unit, the detergency action of the detergent solution scrubs the grit and removes grease, hydrocarbons and dirt therefrom, and entrains this in the detergent solution. The grit eventually accumulates in the frustoconical lower end of the whirlpool wash unit 48 and is discharged therefrom by the metering valve 50. The abrasive grit and'd'etergent solution are discharged from the whirlpool wash unit at a metered rate which corresponds to the rate at which fresh detergent solution and contaminated abrasive grit are to be discharged from this tank into the collection tank 105. These so-called hydraulic fines are then recovered and recirculated to the table 94 so as to be retained in the process stream. Usually, less than about 0.5 weight percent of the total abrasive grit on the table 94 will be recycled in this way. The detergent solution, after separation of the hydraulic fines therefrom, can be returned to the feed to the whirlpool wash unit 48.

As abrasive grit accumulates on the table 94, it is picked up by thedrag elevator assembly and car ried upwardly thereby and deposited in the low temperature rotary furnace assembly 126. During this upward movement, water is drained from the abrasive grit. The function of this furnace assembly in. the process of the present invention is an important one. In the furnace, the temperature iselevated to above 1,00( )F, and preferably to between about 1,200F and l ,300F. Concurrently, hot air currents move through the rotary furnace in a direction which is countercurrent with re-' spect to the direction of movement of the abrasive grit through the furnace. The abrasive grit is thus subjected to elevated temperatures such that combustible contaminants which may still be entrained in the grit are burned and converted to light ash materials or gases through the furnace.

An additional function is that small flakes of metallic contaminants are oxidized to metallic oxides of lesser specific gravity, and may thus be entrained in the air currents flowing through the furnace.

Another important function of the furnace is to effect the agglomeration of particles of glassy vitreous contaminants. It is not uncommon for the abrasive grit to be contaminated with very fine particles of glass. At the temperatures prevailing in the rotary furnace assembly 126, the outer peripheral portions of the small particles of glass are softened or plasticized by the elevated temperatures, and the result is that the particles of glass tend to fuse with each other and agglomerate to form relatively large particles of glass. The average particle size of these agglomerated glass particles is larger than the average particle size of the abrasive grit, thus facilitating subsequent separation by screening. The abrasive grit, on the other hand, is usually a material which does not undergo such agglomeration, since it has a much higher melting point and is generally present, for the most part, in larger particles'than the very fine glass, and is more dense than the glass, and is thus not held up by or entrained in the hot combustion gases as are the glass particles. Moreover, the residual moisture in the mass of denser, larger abrasive grit particles tends to cool these particles so that they emerge from the furnace at a relatively cool temperature in general at about 400F.

A final function of the low temperature rotary furnace assembly 126 is to remove entrained moisture from the abrasive grit. Thus, the moisture is evaporated and passes with the hot air currents through the duct.

142 to the cyclone 144. Here, a final separation is effected to again pick up any very light, extremely fine or small particles of abrasive grit (less thanabout 42 microns in diameter). These are removed in the cyclone 144 and recovered as an abrasive grit fraction of very small particle size. Abrasive grit of this size has many special usages, and for this reason, is an especially valuable fraction of the grit. The air stream delivering the fine particles of abrasive grit to the cyclone 144 is then passed through a filter 146 where any entrained light materials not removed by the cyclone 144 are removed. The relatively clean air stream is discharged to ration to remove ferrous metals from the abrasive grit,.

and to screening to remove the relatively large agglomerated particles of silica from the smaller particles of abrasive grit.

The described process and apparatus for reclaiming abrasive grit has proven to be a highly efficient procedure for restoring abrasive grit, and particularly aluminum oxide, to the state of purity which characterizes this material prior to initial use. The highest industrial standards of purity for such grits can be met by the product of the process of the invention. After cleaning and regrading the material, it is suitable for usage in grinding and lapping compounds, wet honing compositions, mounted grinding stones and wheels, and substantially all other uses to which the original material may be put.

Although a preferred embodiment of the invention has been herein described in order to illustrate the principles of the invention sufficiently for those skilled in that various changes and modifications in the described apparatus and process steps can be effected without departure from these principles. Changes and innovations of this type are therefore deemed to be circumscribed by the spirit and scope of the invention, except as the same may be necessarily limited by the appended claims or reasonable equivalents thereof.

What is claimed is: 1. A process for reclaiming aluminum oxide abrasive grit comprising:

contacting the grit with a detergent solution to remove grease and dirt therefrom; passing grit and detergent solution onto a rotating, first flotation table to remove light contaminants and a major portion of the detergent solution therefrom by density difference; recycling a major portion of the detergent solution to the point of initial contact with the grit; passing the grit having residual detergent solution thereon onto a second flotation table; directing clean .water into the grit; floating residual detergent solution, light contaminants and fine abrasive gr-it away from the relatively larger particles of abrasive grit; recycling said fine abrasive grit into the path of clean water directed into the grit atop said second flotation table; draining a major portion of the water from the grit;

passing the'grit and any entrained contaminants into a heated zone having a temperature exceeding 400F to vaporize moisture on the grit and soften silica particles; and

while the grit is in the heated Zone, passing heated air countercurrent to the direction of travel of the grit in said zone to remove water vapor and light contaminants from the grit;

removing fine particles of abrasive grit from the heated air passed countercurrent to the direction of travel of the grit in said zone; and

separating agglomerated silica particles from the grit after removal of the grit from said heated zone.

2. A process as defined in claim 1 and further characterized as including the steps of;

screening relatively large particles of impurities from the abrasive grit prior to contacting the grit with the detergent solution; and

conveying airborne abrasive grit fines from a locus above said screening step into the mixture of grit and detergent solution on said first flotation table.

3. Apparatus for reclaiming abrasive grit comprising:

1 1 a confining lip around the periphery of said flotation table; and means for receiving detergent solution and contaminants flowing over said lip from said flotation table;

means in said whirlpool washing unit for metering the flow of grit and detergent solution from said whirlpool washing unit to said first rotary flotation table assembly in correlation to the rate at which grit and aqueous detergent solution are introduced to said washing unit;

means for conveying airborne abrasive grit fines from said hood to said rotary flotation table;

a second rotary flotation table assembly positioned to receive grit from said first rotary flotation table assembly, said second rotary flotation table assembly including:

a second rotary flotation table having an upwardly facing surface;

a cone centrally positioned on the'secondflotation table;

a confining lip around the periphery of said second flotation table; and

means for receiving rinse water and light abrasive grit fines flowing over said lip from the flotation table in said second rotary flotation table assembly;

.a grit conveying chute interconnecting said first and second rotary flotation table assemblies for receiving grit from said first rotary flotation assembly and conveying it to said second rotary flotation table assembly;

water jet means positioned over at least a portion of said chute for directing water against grit in said chute;

a rotary furnace assembly;

an inclined drag elevator extending into immediate proximity to the rotary table of said second rotary flotation table assembly and to said furnace for conveying rinsed abrasive grit from said second rotary flotation assembly to said rotary furnace assembly;

a suction fan for drawing air. through said furnace assembly;

means for heating the air drawn through said furnace assembly; and

a cyclone separator interposed between said furnace assembly and said suction fan.

4. Apparatus as defined in claim 3 wherein said grit conveying chute has an open intake end immediately adjacent the upwardly facing surface of said second rotary flotation table inside said lip, and hasan intermediate portion extending over said lip and thence downwardly therefrom;

and said water jet means is positioned over said second rotary flotation table and adjacent the open intake end of said chute for moving grit from said second rotary flotation table into said chute. 

2. A process as defined in claim 1 and further characterized as including the steps of: screening relatively large particles of impurities from the abrasive grit prior to contacting the grit wiTh the detergent solution; and conveying airborne abrasive grit fines from a locus above said screening step into the mixture of grit and detergent solution on said first flotation table.
 3. Apparatus for reclaiming abrasive grit comprising: a rotary vibrator screen for separating relatively large particles of impurities from said abrasive grit; a hood around said rotary vibrator screen; a whirlpool washing unit positioned to receive grit discharged from said rotary vibrator screen; means for introducing an aqueous detergent solution to said whirlpool washing unit; a first rotary flotation table assembly positioned to receive grit and detergent solution from said whirlpool washing unit and including: a rotary flotation table; a cone centrally positioned on said rotary flotation table; a confining lip around the periphery of said flotation table; and means for receiving detergent solution and contaminants flowing over said lip from said flotation table; means in said whirlpool washing unit for metering the flow of grit and detergent solution from said whirlpool washing unit to said first rotary flotation table assembly in correlation to the rate at which grit and aqueous detergent solution are introduced to said washing unit; means for conveying airborne abrasive grit fines from said hood to said rotary flotation table; a second rotary flotation table assembly positioned to receive grit from said first rotary flotation table assembly, said second rotary flotation table assembly assembly a second rotary flotation table having an upwardly facing surface; a cone centrally positioned on the second flotation table; a confining lip around the periphery of said second flotation table; and means for receiving rinse water and light abrasive grit fines flowing over said lip from the flotation table in said second rotary flotation table assembly; a grit conveying chute interconnecting said first and second rotary flotation table asemblies for receiving grit from said first rotary flotation assembly and conveying it to said second rotary flotation table assembly; water jet means positioned over at least a portion of said chute for directing water against grit in said chute; a rotary furnace assembly; an inclined drag elevator extending into immediate proximity to the rotary table of said second rotary flotation table assembly and to said furnace for conveying rinsed abrasive grit from said second rotary flotation assembly to said rotary furnace assembly; a suction fan for drawing air through said furnace assembly; means for heating the air drawn through said furnace assembly; and a cyclone separator interposed between said furnace assembly and said suction fan.
 4. Apparatus as defined in claim 3 wherein said grit conveying chute has an open intake end immediately adjacent the upwardly facing surface of said second rotary flotation table inside said lip, and has an intermediate portion extending over said lip and thence downwardly therefrom; and said water jet means is positioned over said second rotary flotation table and adjacent the open intake end of said chute for moving grit from said second rotary flotation table into said chute. 